.box {
  position: relative;
  margin: 30px;
  width: 450px;
  display: inline-block;
}
.img {
  width: 450px;
  height: 450px;
  border: 1px solid #333;
  position: relative;
  background: url(./imgs/1.jpg) no-repeat;
}
.img > .mask {
  width: 200px;
  height: 200px;
  background-color: yellow;
  opacity: 0.4;
  position: absolute;
  top: 0px;
  left: 0px;
  display: none;
}
ul {
  display: flex;
  list-style: none;
  margin-top: 10px;
}
ul > li {
  width: 54px;
  height: 54px;
  border: 1px solid #333;
  margin-right: 10px;
  cursor: pointer;
}
ul > li.active {
  border-color: red;
}
.enlarge {
  width: 400px;
  height: 400px;
  position: absolute;
  top: 0;
  left: 101%;
  background: url(./imgs/1.big.jpg) no-repeat;
  background-size: 800px 800px;
  background-position: 0 0;
  display: none;
}
